Peter Berg wrote:@Louis,
First of all, a 4" system is not easy to implement, very few do exist and running succesfully. Using a 4" stove pipe for the heart of the thing will lead to disappointment, when the thing is running as it should the pipe would hold out one month, tops. See a short but recent discussion on the same topic here.
Also, in a small two person's caravan there wouldn't be much room to implement a full scale bench system, I reckon.
And cooking on the top surface of the drum even in summer? I doubt that. Unless... you make the barrel interchangable for one which is shorter as the normal one, the minimum distance from riser end to top of the barrel, thus creating a really hot spot in the middle of the drum top. In addition, I've found out that when the stove is running healthy, throughout the innards there's a slight underpressure. This way, it would be possible to run it with small leaks during cooking. It proved possible to undo the bung hole at the top of a full running stove and film through the hole without the CO detector kicking into alarm. It would be sensible to buy a CO detector anyway.
I do agree with Allen at the points of using very dry and thin split wood and downloading the Rocket Mass Heater book by Ianto Evans and Leslie Jackson.
The exhaust pipe will come out at a low level. Leading it outside and up will automatically mean you have to insulate the whole of the outside stack. It would be better to lead the pipe straight up from the exhaust spot in single wall pipe and change to triple wall pipe under the ceiling and out.
A suggestion: look into the possibility of purchasing a ready-cast 4" core. That would take the difficult part of the job out of your hands, so you are free to concentrate on implementing a reasonable efficient heat conducting system around it. I am biased about this core, so when you decide to try it all by yourself, please do.